The invention comprises improvements in the structure of confining surfaces, passages or chambers subject to contact by highly heated gaseous fluids as in the combustion chambers or generating channels in Magnetohydrodynamic (MHD) Electrical Power Generators and the like and particularly relates to reduction of the area of fixed confining surfaces presented by materials subject to excessive erosion or corrosion through contact with moving high temperature gaseous fluids sometimes carrying solid particles or "seed" which increase the eroding effects of the gaseous fluids themselves.